Horace was Acceptable at Charms, Exceeded Expectations in Transfiguration, and was Outstanding in Potions.
Average is what it all added up to when he did the maths. Average was going to get him nowhere. His successes had to be highlighted. His triumphs had to overshadow his faults.
The rumors of Horace's perfect Potions score spread like wildfire throughout the school, and when he looked at his Outstanding grade, he had no reason to believe it wasn't true.
And when the third year boy approached him with a box of sweets, asking for tutoring, Horace knew he had found his calling.