If you do not want to claim him as your dependent then do not enter his personal information in the My Info section of the program.
Since is he is eligible to be claimed as a dependent, If he is filing a tax return he will have to indicate on his tax return that he Can be claimed as a dependent even if no one is actually claiming him as a dependent.
He will not be eligible for a stimulus payment since he can be claimed as a dependent. He will not be able to enter any education expenses on his tax return since he can be claimed as a dependent.
if you are not releasing the child's exemption to the noncustodial parent the tax laws do not require you to claim him as a dependent. However, the tax laws DO REQUIRE him to mark that he CAN be claimed as a dependent on his return. To NOT CLAIM Him on YOUR return just delete the dependent worksheet for him. this will prevent you from getting any deductions or credits that require you to have a dependent. Not the least of which is that you will have to file as single rather than head of household if you are not married.
if you are releasing the child's exemption to the noncustodial parent you can still claim head of household.