If he is not at his max dose, it may be that a dose increase is needed. If it cannot be increased, maybe adding guanfacine (Tenex) would be enough to get back on track. Alternatively, a low dose of stimulant plus guanfacine might avoid or lessen the tics and give symptom relief. Look on the medication board for the 7+ page thread called "Tenex" (guanfacine is the generic for tenex) for information on this non stim med for ADHD and for treatment of tics.
What is the dosage of Strat, ? What is his weight?
Straterra is dosed at 1.2-1.8 mgs per kilo, and will not work well if the dose is too high or too low.