I think the fact that it helps right after he takes it but wears off fast is due to it being short-acting. It’s not ideal.
But, yes, it’s common to have to change dosage and/or medication as kids grow. Not necessarily due to the change in size, since that’s not a factor in dosing stimulant medications, but because they change and their neurotransmitters change, and hormones are added, etc…
Dr. William Dodson advises against increasing the dosage just to solve duration problems in this article: https://www.additudemag.com/adhd-medication-11-steps-for-prescribing-it-effectively/.
Definitely talk to the prescribing doctor and see what you can do to secure more effective treatment for your son again.
ADDitude Community Moderator, Author & Mentor on Parenting ADHD, Mom to teen w/ ADHD, LDs, and autism