Final answer:
Jeffrey was Anna's partner when the class tested different substances on plants in the book 'Because of Mr. Terupt'.
Step-by-step explanation:
In the book 'Because of Mr. Terupt', Anna's partner when the class tested different stuff on plants was Jeffrey. Jeffry was paired with Anna to observe and record the effects of different substances on the growth of plants. Their experiment was part of a larger science project led by their teacher, Mr. Terupt.