I'm wondering why these sentences begin with "a" instead of just "este estudiante". Does anyone know?

A este estudiante le gusta la historia.
Al niño no le gusta jugar de tenis.
A las mujeres le gustan té.

Thanks!

The phrase that begins with 'a' clarifies (names/gives emphasis to) the indirect object pronoun. In each sentence you provided, the indirect object pronoun 'le' is used. This pronoun, by itself, could be transliterated as 'to him/to her/to you/to it'. The phrases that begin with 'a' are simply clarifying 'to whom' the pronoun referred.

This is why, when a native Spanish speaker is starting to learn English, she often says, "The women, they like tea," instead of, "The women like tea." In Spanish, both the indirect object pronoun AND the 'a' phrase are needed to make the sentence clear and grammatically correct.

By the way, the second sentence should read: Al niño no le gusta jugar al tenis.
The last sentence should read: A las mujeres les gusta el té."