It was Barty Crouch Jr who attacked Harry if I remember correctly and he's much more skilled than Peter. You have to remember though that Harry is holding back when dueling the students. He uses fancy combos to push and annoy Gabrielle and most of the other students are simply swept aside like it's nothing. A lot of people here are saying that he's progressing too fast but I don't really think that's much of a problem given how conceptual the magic is. Some people are simply brilliant in ways that most of us can't match and that counts even more with magic than normal subjects in my opinion. Also, don't forget that Voldemort managed to make a damn horcrux in his 5th (?) year. That's some serious magic right there. And Harry is supposed to be on par with him.