I think your son need a teacher because no one can play perfectly. Everyone makes mistakes, even a good pianist too… A teacher needed to critic his performance, give him advice, and improve his skill.

If I understand your question correctly, you’re asking us:

Because you can’t afford to finance professional instruction for him to prepare for “Abram diploma”; you want him to self-prepare, and try for it? Is that correct?

If so, how he feels about it would be more important than how any of us would; have you discussed this with him?

And have you discussed this with his teacher, or some other qualified academic?

If not, I would highly recommend you do both; before arriving at any ultimate decision in the matter.

And I personally unless you got the go-ahead both from your son and a qualified professional, I would let it go: forget it.

Nothing can destroy a youngster’s self-esteem more than being pushed beyond their limits, and then failing.

Good luck, but be careful,

Alberich

You really need a good teacher, if budget is a problem, look for a scholarship program in preparatory division in music conservatories, if he is really talented, he will get lessons for free.

A good teacher is important so he doesn’t develop bad habits, very hard to fix. And a good teacher can help him mature musically.