The Luther Thorne Memorial Primary student scored 97 per cent in English and 98 per cent in maths, for a total of 254.31 B.
When the DAILY NATION visited her at school yesterday, she was not yet aware of her achievement and was overjoyed when she received the good news.
"I knew I did well but I didn't think I did this well," she said.
Powell, who lives at 224 Husbands Gardens, St James, said she felt nervous when she started the exam but quickly lost her nervousness, as she found the maths easy and the grammar even easier.
She is part of a tradition, as she has not one, but two brothers already attending Harrison College.
"I spent up to three hours a day studying and looking at past papers, but it wasn't hard, as I always wanted to go to Harrison College," she said.
Her father, Grenville Powell, was nearby when he received the call and quickly arrived to congratulate his daughter.
He said he expected her to be the top student at Luther Thorne and to pass for Harrison College, but did not expect she would have been the best in the island.
Rosetta Yearwood is the teacher behind Powell's success. She said she knew her student would be going to Harrison College.
"She is an excellent student with excellent study habits. I did not have to push her at all."
Principal Anthony Jordan was "ecstatic" at Powell's success, as the school was narrowly edged out last year.
He said they were "trying for years to get someone in the top spot and were adamant to get it done this year".
"We always aspire to having the top students. Our motto is: Strive Always For Excellence and it is always in the forefront," he said.
Jordan added that, despite public perception, the school was actually not a "Common Entrance workshop" but offered excellent, well-rounded and varied extra-curricular activities as well.