Lily and James never realised that their child was a superb ventriloquist, they went to their deaths ignorant of that fact. It was in fact his ventriloquism that saved Harry the night that Voldemort came to kill him. There was a mirror on the back of his bedroom door, and after he heard Voldemort utter the words that killed his mother, he threw his voice behind Voldemort, who, hearing the start of the killing curse coming from behind him, spun around cast a reducto, which was reflected by the mirror back at him.
During the ten years he spent at the Dursley's he used his gift many times, to get Dudley into trouble and himself out of trouble. Poor Vernon did not have much peace, with constantly having to deal with requests from Petunia and Dudley.
It was at his sorting at Hogwarts however that he really started to have fun. With a view to the future, any girl he found cute, heard the Hat shout out Gryffindor, as soon as it touched their head. However, regardless of appeal, as he found Hermione obsessive about her studies, he put her in Ravenclaw. As Malfoy was such a ponce, he remembered his claim to quit if put in Hufflepuff, so he put him there. At the end of the sorting the only House with more than two girls in it, was Gryffindor, which coincidentally only had two boys, Harry and Ron.
After the third Potions class, he realised that Snape really hated him, it had only taken one lesson to learn that Quirell was a waste as a teacher, so he developed a plan to remove both of them. One day he got the chance to use the plan, as Snape was walking down a corridor a few paces behind Quirell, who had his wand in his hand Quirell heard Snape's voice starting the incantation for the killing curse and spun around, casting a reducto (fewer syllables), before realising that Snape's wand was not in his hand. Snape died and Quirell was taken in for questioning.
Fortunately for Harry, Quirell's possession was not happy with the questioning, and chose to leave Quirell in the Ministry, in front of Madame Bones and other Department Heads. Whilst they were uncertain as to who the spirit was, they knew there was a spirit possessing a teacher at Hogwarts. Within a week, the Headmaster was forced to go over the castle's wards, and restore or place wards for such things as possession, animagus and polyjuice, as well as the Dark Mark. He could no longer use Snape as an excuse, as Snape was dead.
In the Gryffidor dorms, a plot was afoot. Females with Slytherin, Hufflepuff and Ravenclaw attitudes had been studying Harry, and were not happy, the first step was to separate him from Ron Weasley, so as to remove a poor influence on his study habits. The second move was to get him to withdraw funds from Gingrott's, and having measured him, send for clothes that fit him, pointing out to him, that if he was concerned about his relatives, leave the new clothes with one of them, and use the old clothes during the summer vacation, the only time he would be back with the Dursleys. Anther plan was immediately formed to investigate why no one had checked on the poor treatment he got from the Dursleys.
Whilst these plans were unfolding, Padma Patil, who had been put on the team to keep Ron distracted, was thinking about why a ten year old rat was looking so healthy. She wrote to her parents, who after talking with an animal healer, wrote back to state that it could be a person, transfigured or an animagus. She spoke with her House Head, and the next day in front of the whole house, Scabbers changed into a man, who Professor McGonagall identified as Peter Pettigrew.