Learn Portuguese (Portugal): Temos oito alunos e nove alunas na escola. - We have eight male students and nine female students at the school.

No, the numbers from 3 to 10 do not change based on gender. So it is oito alunos and oito alunas, and the same goes for nove. However, remember that the numbers 1 (um or uma) and 2 (dois or duas) do change depending on whether the noun is masculine or feminine!

Why does the sentence say alunos e alunas instead of just using one word for 'students'?

In Portuguese, if you have a mixed group of male and female students, you normally just use the masculine plural: alunos. But here, the speaker is specifically counting the boys and girls separately, so they use the masculine alunos for the males and the feminine alunas for the females.

Where is the word for 'we' in this sentence?

The word for 'we' is nós, but it is left out here. In Portuguese, the verb ending usually tells you who is doing the action. The verb temos only ever goes with nós, so the pronoun is not needed unless you really want to emphasize it.

Why is it na escola instead of just em escola or em a escola?