How do you say grade 3 section A pupils spanish?

There isn't a single perfect translation as the phrasing depends slightly on the context and the specific Spanish-speaking region. Here are a few options:

* Alumnos de 3º de primaria, grupo A: This is a formal and widely understood option. `3º` means 3rd, `primaria` means primary school, and `grupo A` means group A.

* Niños/Niñas de 3º de primaria, sección A: Similar to the above, but using `niños` (boys) or `niñas` (girls) or both, making it slightly less formal. `Sección A` is another way to say section A.

* Clase de 3º A de primaria: This translates to "3rd A grade class" and is more concise.

* Los alumnos/as de tercero A: This is a more informal option using "tercero" (third) and implying "primary" as it's the usual context for grade 3. The `/as` indicates inclusivity of both genders.

The best option depends on your audience. For official documents, the first option is preferable. For informal conversations, the last option might be more suitable.