。
She tailored her teaching to the slower learners.
Literal
She [topic-は] teaching-method [object-を] learning [genitive-の] slow students [to-に] adapted.
Several pieces work together. 教え方 uses the productive ~方 ('way of doing') suffix on the masu-stem of 教える: 'way of teaching.' Same pattern: 食べ方 ('way of eating'), 歩き方 ('way of walking'), 考え方 ('way of thinking'). 学習の遅い ('slow at learning') is an adjective phrase modifying 生徒 — note the inner subject 学習 takes の rather than が in this prenominal position (が→の conversion in relative clauses). 合わせる ('to adjust, fit X to Y') takes the matched-to target with に.