One Of THOSE Days...

...or, to be more specific, one of the days on which Murphy's Law demonstrates its existence.

First lesson of the day. I have a student teacher in class with me. I'm prepared. I manage to get to the Science lab before my class arrive (they're still in assembly, which has overrun.) The practical equipment is on the front bench. I set up my computer to connect with the smartboard...

First glitch: the board refuses to orient itself, and so I can't actually write on the smartboard.

Quickly I put the computer away and write the title and date on the miniscule white board.

I then turn my attention to the practical equipment. It isn't quite what I had expected, so I examine the tray more carefully.

Second glitch: the practical equipment is actually for another teacher, for the following lesson, on a similar but different topic.

The class has, by this time, arrived in the lab. I grab the sheets I had intended to give them for homework, distribute them to the class with instructions for completion, and dispatch the student teacher to the prep room in search of the practical I actually ordered.

Luckily it has just been forgotten behind the prep room door, and is easily retrieved.

At the end of the practical, I ask for a quick show of hands to discuss the results. How many students found that their starch solution was digested by the boiled enzyme? (For the non-scientists among you, the starch should not be digested by the boiled enzyme, as high temperatures denature and inactivate enzymes, which are biological catalysts.)

Third glitch: all the students put up their hands to show that digestion was successful.

I exchange glances with the student teacher. One or two pupils might have made mistakes, but not all of them... it is possible, however, that the solutions were mixed up...

So, I test a small sample of the starch without any enzyme. It turns black when iodine is added. All well and good. I mix the starch with the normal enzyme, and add iodine. No change. All as it should be. I mixed the starch with the boiled enzyme... and add iodine. No change... which means that either someone, somewhere, has invented a super-enzyme which can withstand boiling (which will make me lots of money when I sell it to washing powder manufacturers) ... or, alternatively, that someone forgot to boil the enzyme...

Why is it that this sort of thing only ever happens when I'm being observed by another adult who is taking notes?