sounds like the heater is either not owrking properly, or might have worked loose.

I too have a ctc i3 pro b on a tall shelf :-)
The difference is I bought it to play with and don't actually need it.

But sounds like yours is not coming to temp properly to me.

Check the heater cartridge, they can work loose over time.
Mine did on the sapphire.

If I had not glanced over and spotted this red hot glowing cylinder behind the print carriage - things could have got nasty !

Also check the thermistor is working properly and also has not worked loose.

Impressed that your son is at a school sensible enough to have 3d printers.
That's pretty cool :-)