tricot:
this is tricky terrain. If you come in with suggestions for alternatives to computer time you may come across as complaining/ pushy.
I think the first thing is to be absolutely certain the games he is playing are not educational.
If he's playing minecraft for more than 1 hour a day - do not pass go, just complain. That's outrageous.
If, however, he's playing an addition game, a spelling game, etc... whilst others finish their work and he's learning more things - well it may not be ideal, but it probably won't cause much harm.
Pedagogically, however, there should be work to keep him engaged so some suggestions:
Maths: could the teacher give him an age appropriate/ ability appropriate nrich maths puzzle to solve from lower primary section?: nrich.maths.org/frontpage - these can be printed out in advance and worked on away from a computer screen.
Reading: could the teacher allow him to read from his own book - or go to the library to get another book if finished with his current book/ and done with reading work in class?
Writing: could the teacher ask him to write more or do another task?
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Every school is different but our present primary (DD2 moved schools in Y4) and a friend's school both handle this by letting more able pupils access more challenging work.
Friends school actually has blocks of time for maths/ literacy - and more able pupils can join an upper school year if they are working securely at the next year's general ability level.
Our school handles it by providing work at 3 ability levels: everyone should be able to do this/ a bit tricky/ will melt your brain. Children also have colour cards so if they're struggling they hold them up. If you're finished with your sheet & have done well - you move up to the next sheet. The 'will melt your brain' puzzles (often from nrich) will keep them entertained for quite a while - so there never seems to be an issue of someone finished with nothing to do.
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I wouldn't blame the NQT for this policy - it is unlikely that this reflects their teaching style - it probably is a school wide approach. Many schools give the impression they resent upper ability pupils and the demands it places on staff to prepare work in a wide range. To be fair to teachers if you're coping with everything from NC L3 - NC L6 (as DD1's poor Year 6 teacher was) it is a lot of work to make resources for those upper ability kids - many of whom are doing more at home anyway and are happy to sit and read a book whilst their classmates finish up their work.
One could go on about the waste of potential - and it is- but I do understand that the pressure on primary schools (due to performance table statistics) is to get as many as possible over that NC L4 threshold and, therefore, the focus of effort naturally falls on those pupils below that ability. At present there is no reward for schools expending energy on helping an able NC L4 pupil achieve NC L5 or an able NC L5 pupil achieve NC L6.