"Františku, jsi stále studentem?"

[tbiedl]

Can you explain why this is "studentem" here? What would "jsi stále student" mean (if it makes sense at all)?

[kacenka9]

To be somebody or something is used with both Nominative and/or Instrumental cases. Either or. Both are correct. So if you were translating this to Czech 'jsi student' would be accepted.

Though both are correct, the instrumental is slightly more archaic and you would not hear it much, though it might be regional.