Even when it comes to learning, the good student contradicts his teacher and makes him more eager to explain and defend the truth. Challenge someone discreetly and his teaching will be more perfect.

[Y aun para el aprender es treta del discípulo contradecir al maestro, que se empeña con más conato en la declaración y fundamento de la verdad; de suerte que la impugnación moderada da ocasión a la enseñanza cumplida.]

Baltasar Gracián y Morales (1601-1658) Spanish Jesuit priest, writer, philosopher

The Art of Worldly Wisdom [Oráculo Manual y Arte de Prudencia], § 213 (1647) [tr. Maurer (1992)]
    (Source)

(Source (Spanish)). Alternate translations:

In matter of learning it is a cunning fetch in the Schollar to contradict his Master, inasmuch as it lays an obligation upon him, to labour to explain the truth with greater perspicuity and solidity.) So that moderate contradiction gives him that teaches occasion to teach thoroughly.
[Flesher ed. (1685)]

Also in learning it is a subtle plan of the pupil to contradict the master, who thereupon takes pains to explain the truth more thoroughly and with more force, so that a moderate contradiction produces complete instruction.
[tr. Jacobs (1892)]

A good trick on the party of the pupil is to bait his teacher, who thereby excites himself to greater effort in the declaration, and the foundations of this beliefs, whence it comes that well-moderated debate makes for most effective teaching.
[tr. Fischer (1937)]