The effect of learning should be measured through observable performance outcomes. ACMP highlights job performance as the most direct indicator, showing that knowledge and skills gained in training are being applied. Communication (A) and teamwork (C) may improve indirectly, while stress reduction (D) is harder to quantify. Tangible evidence comes when employees perform their roles effectively in the new state, making job performance (B) the correct answer.

(Reference: ACMP Standard, Process Group 3 -- Learning and Development Plan; Activity: Measure effectiveness of training through performance outcomes.)