Is it really Zac Efron singing in high school musical?

Yes and no. Zac Efron does sing in the first HSM but his voice was blended in with Canada's Drew Seeley who played Troy in the Broadway version of High School Musical while Zac was shooting Hairspray. Seeley was not givin recognition for his singing in HSM. But it's all Zac in HSM 2

It was all him Canada Drew didnt have anything 2 do with him. He sounds nothing like him. He just does the tours coz they oviously don't use the real HSM actors on tour they use look alikes!!