Learn Finnish: Arvosanojen ohella arvioimme myös opiskelijan ansiot. - Alongside the grades, we also evaluate the student's merits.

The postposition ohella (alongside / in addition to) requires the word it governs to be in the genitive case. Because we are talking about multiple "grades", the basic word arvosana is put into the genitive plural form, becoming arvosanojen.

Could I use lisäksi instead of ohella in this sentence?

Yes, arvosanojen lisäksi (in addition to the grades) would mean almost exactly the same thing. However, ohella (which stems from an old word for "side" or "edge") sounds a bit more formal and abstract, making it a great vocabulary choice for academic or professional contexts at a B2 level.

The verb arvioida (to evaluate) often takes a partitive object. Why is ansiot in the T-plural here instead?

While you would use the partitive for evaluating an ongoing or partial situation (like arvioimme tilannetta - we are evaluating the situation), here the evaluation is presented as a complete action covering an entire, specific set of things (all of the student's merits). Therefore, it takes a total object. For plural nouns, the total object is formed with the basic T-plural (ansiot).

Does the word ansio always mean "merit"?