Medication isn’t just for work/school performance or being able to follow rules and instructions. It helps all areas of life that ADHD affects. Therefore, by decreasing your dose during the summer, you may be increasing symptoms.
Tolerance to the therapeutic effects of stimulants is actually rare. You might want to consider talking with your doctor about keeping the same dose during the summer in order to meet your goals for the summer. Also, it helps to think ahead of time what you want to do with your summer. Indecisiveness is a bigger deal when trying to decide in the moment.