The teachers are all running at the start of the game.

The jumping sound effect is not as it should be, because of an erroneous CALL instruction in the routine at EAEB.

POKE 60149,254

Usually, when a character is walking he will cycle through walking animation phases 1, 2, 3 and 4. So, for example, when MR WITHIT is walking leftwards, his animatory states will progress thus (reading from right to left):

However, when a character is looking for ERIC and walking leftwards, he will cycle through walking animation phases 1 and 2 only, or phases 3 and 4 only. For example, when MR WITHIT has left the Map Room to hunt down the truant ERIC, his animatory states cycle thus (through phases 1 and 2) as he makes his way leftwards across the bottom floor:

And when MR WITHIT has left the White Room to hunt down the truant ERIC, his animatory states cycle thus (through phases 3 and 4) as he makes his way leftwards across the bottom floor:

The reason for this shortened cycle of walking animation phases is the lack of symmetry between the routine at 7BFB (which is responsible for moving ERIC's chaser from the midstride position) and the routine at 7C18 (which is responsible for moving ERIC's chaser to the midstride position). The routine at 7BFB decrements the animatory state if the chaser is moving leftwards, and increments it if he's moving rightwards. However, the routine at 7C18 always increments the animatory state, regardless of the chaser's direction of travel. Thus the chaser's walking animation phases get locked into a 1-2-1-2 or 3-4-3-4 cycle if he's moving leftwards.

Usually, when a character is going up a staircase he will cycle through walking animation phases 1, 2, 3 and 4 thus:

However, because of a bug in the routine at 65E4, when ERIC is going up a staircase he cycles through walking animation phases 1, 4, 3 and 4 instead thus:

POKE 26138,4

ERIC can be knocked out by BOY WANDER's catapult pellet even when he's sitting on the floor or is already lying on the floor (and the pellet should really fly straight over his head instead). The best way to reproduce this bug is to stand (or sit) in BOY WANDER's line of fire in a classroom while everyone's waiting for the teacher to show up for the lesson.

In lesson 0xE3 (MR ROCKITT - EXAM ROOM), little boys 4-8 head off to the White Room in accordance with their personal timetables, but no teacher ever arrives to start the lesson.

POKE 42723,134 (sends MR CREAK to the White Room)

Before wiping the board and getting a lesson under way, ERIC's teacher will wait for EINSTEIN to sit down first: see 7CD0. This makes sense at the beginning of a lesson, but that same routine is called several times during the course of a lesson (see F300) to check whether ERIC is present, which means that the teacher will also stop whatever he's doing and wait for EINSTEIN to sit down before continuing on those occasions too. This is not really noticeable except during lessons where there is no question-and-answer session taking place between the teacher and the swot, and the teacher is pacing up and down in front of the blackboard instead. During those lessons, the call to 7CD0 is made each time the teacher has reached the point where he is just about to turn round; if EINSTEIN is not sitting in a chair at that time (because ERIC has pushed him out of his seat, for example), the teacher will wait until EINSTEIN is back in his seat before turning round.

This phenomenon can be made more readily reproducible and observable by using the following POKEs:

Many command lists use the routine at 7C47 to trigger a restart. This works as expected when the current lesson appears in the main timetable, but does not work during the 'special' playtimes - 0xF3, 0xF4 and 0xF5 - which do not appear in the main timetable, but instead replace main timetable playtimes at random three times out of eight on average (see 6E33).

The problem is that the routine at 7C47 looks up the current lesson (whose number is stored at 7FF9) in the main timetable in order to find out which command list to restart, and then copies the start address of that command list into bytes 0x77 and 0x78 of the character's buffer, overwriting the command list start address that was already there.

The most noticeable effect of this bug will occur during a special playtime that has replaced a 'stampede' playtime (0xFC or 0xFD). Little boys 1-9 and 11 (not 10, because he's busy looking for ERIC to tell him what's going on) start with command list 196 (walkabout), but when the restart command is reached, will switch to command list 0xCC (stampede leader) or 0xCE (stampede follower). Thus a special playtime in which ERIC must watch out for ANGELFACE, BOY WANDER or EINSTEIN is complicated by the presence of stampeding boys tripping everyone up.

If ERIC has exactly 10000 lines, MR WACKER will come rushing to ERIC's side and say "YOU HAVE OVER 10000 LINES TO WRITE ERIC..." (see F9BB). Does the headmaster not know how to count, or does he actually think that 10000 > 10000? Either way, this is poor form for a maths teacher.

POKE 63943,233 (keeps MR WACKER at bay until ERIC's lines total exceeds 10000)

By using the undeliverable message technique, it is possible to avoid being sent home by MR ROCKITT (when ERIC has mumps) or MR WACKER (when ERIC has 10000 or more lines).

If MR ROCKITT is on his way to send ERIC home, head for the nearest blackboard and press 'W' to start writing. Then wait. And wait some more. And wait some more on top of that. After about 20 minutes, the bell will ring, at which point it will be safe for ERIC to stop writing (press ENTER). MR ROCKITT will walk away, having apparently forgotten all about ERIC's disease.

Likewise with MR WACKER. After the bell rings, press ENTER to finish writing on the board and MR WACKER will walk away, having lost interest in sending ERIC home. However, ERIC must proceed with care: the next time he gets lines, MR WACKER will come looking for him again.

When ANGELFACE has mumps, ERIC may be able to run past him without 'touching' him, and thus avoid contracting the disease.

This trick is possible because the collision detection code at FA2A is executed only during ANGELFACE's turn to move; ERIC moves faster than any other character in the game, and so if he times it right, he can scoot past the bully in between his turns to move.

In lesson 0xE5 (REVISION LIBRARY), MR ROCKITT paces up and down in the Exam Room like a little boy, waiting for a teacher who never arrives.

POKE 42213,188 (sends MR ROCKITT to the staff room)

When a speech bubble is obscuring a shield, ERIC cannot get it by jumping up to it or firing at it. This is because the routine at 6DEF checks for the presence of a shield at the location of ERIC's hand or pellet by inspecting the attribute byte: a shield is assumed to be present only if neither the PAPER nor the INK is black. However, when a speech bubble is in the way, the INK is black, and the routine exits early.

Speech bubbles are vulnerable to corruption by the movement of characters or catapult pellets in front of them. The easiest way to see this is to climb the stairs that lead up to the head's study when a teacher is standing at the doorway of the White Room telling the kids to sit down. (This bug was fixed in Back to Skool by ensuring that characters, pellets, etc. are always drawn behind speech bubbles instead of in front of them.)

ERIC's teacher and EINSTEIN can hog the 'speech queue' for several rounds of a question-and-answer session, making the other teachers wait a long time - sometimes until after the bell has rung - before they can tell the kids to sit down or what to do during the lesson.

The reason this can happen is that there actually is no speech queue. That is, there is no mechanism for recording whose 'turn' it is to speak next.

Consider the case where ERIC is being taught by MR CREAK in the White Room, and MR ROCKITT is teaching in the Exam Room:

• MR CREAK is asking a question
• EINSTEIN is waiting for MR CREAK to finish speaking
• MR ROCKITT is standing at the blackboard, waiting to tell the kids what to do

When MR CREAK finishes speaking, the character-moving routine at 6226 considers moving the following characters (after MR CREAK) in this order:

• BOY WANDER
• ANGELFACE
• EINSTEIN

A character will be moved if bit 7 of byte 0x7A of his buffer is reset (which is true for kids half the time on average, and true for teachers only when they're running), or if byte 0x7B of his buffer (which is decremented on each pass through the character-moving routine) holds an even number. If either of these is true for EINSTEIN, he will get to speak next. When he's finished answering MR CREAK's question, the character-moving routine considers moving the following characters (after EINSTEIN) in this order:

• little boys
• MR WACKER
• MR ROCKITT
• MR WITHIT
• MR CREAK

If, on MR ROCKITT's turn, byte 0x7B of his buffer holds an odd number, he will not be moved, and will therefore not start speaking before MR CREAK. If, on MR CREAK's turn, byte 0x7B of his buffer holds an even number, he will be moved and therefore start speaking before MR ROCKITT's next turn.

Thus MR ROCKITT could spend quite a while waiting at the blackboard before telling the kids what to do, all depending on the contents of byte 0x7B of his, MR CREAK's and EINSTEIN's buffers (and also bit 7 of byte 0x7A of EINSTEIN's buffer) on their turns to be moved.

Kids are unable to sit in the back seat in the Reading Room (see 6BF0). This may actually be a feature, though, because if EINSTEIN sits in the back seat, his speech bubble goes through the wall into the Map Room.

POKE 27704,56

The blackboard buffers are wiped before a new game (or demo mode) starts, but the blackboards themselves are not. Thus BOY WANDER, who would normally write only on a clean board, will unwittingly scrawl over a blackboard's previous contents at the start of a new game. (This bug was fixed in Back to Skool.)

'Phosphorous' (at E0BC) is misspelt; it should be 'Phosphorus'.

Lesson 0xE6 (REVISION LIBRARY) has MR CREAK teaching an empty class in the Reading Room.

POKE 42726,188 (sends MR CREAK to the staff room)

If ERIC hits a character who is sitting on a chair, and then quickly sits in the chair just vacated, ERIC will not be pushed out of the chair when the character rises and takes his seat again.

In lesson 0xEC (MR WACKER - WHITE ROOM), BOY WANDER is in the Revision Library (on his own, as it happens). However, if EINSTEIN tells on BOY WANDER for writing on the board, MR WACKER will still give lines to the absent tearaway. (Perhaps the ceiling in the White Room conducts sound well enough for BOY WANDER to hear the admonition.) The same thing may also happen in lesson 0xED (MR WITHIT - WHITE ROOM), when BOY WANDER is once again in the Revision Library (this time accompanied by ANGELFACE).