Five possibilities for this come to mind right away:
1) Poor executive functioning – could cause him to lose his place in calculations. (common with ADHD) If the test is long, overwhelm “paralysis” could be at play.
2) Working memory deficits – could cause him to make mistakes in calculations (common with ADHD)
3) Dyscalculia (math LD) – while the fact that he does homework well may make this less likely, it depends on how much support and assistance he’s getting with homework. If he can do the math with lots of help, but not when it’s solely up to him, this is possible.
4) Format of tests – I find this to be a huge issue for my son. For example, he does terrible with multiple choice tests and says he could do better if everything was short answer.
5) Test anxiety – while you’d think he’d struggle with tests in all subjects if it were test anxiety, the fact is that he could be super anxious about math tests because he struggles with them, but at easy with other exams because they are easier for him.
Medication could help if it’s a focus problem or an anxiety problem. Medication won’t do much, if anything, for the other possibilities.
ADDitude Community Moderator, Author & Mentor on Parenting ADHD, Mom to teen w/ ADHD, LDs, and autism