My question is this. When you write a scale with accidentals do you add the accidental once when it's ascending or both times when it's ascending and descending? So are you supposed to write the accidental two times when writing a scale? In the same bar. Google is confusing me.
Usually a scale is in a certain key. In this case there are no accidentals, because the sharps or flats are notated as key signature right at the beginning of the system between the clef and time signature.
If you write a scale without key signature it depends on the note values, because the accidentals are only valid in the measure they are marked. If the descending scale is in a new measure you have to notate the accidentals anew.
If this is a task to demonstrate your knowledge of the scales and you don't use bar lines (as there is no rhythm), you can notate the scale up and down in whole notes, half notes, quarter notes etc. all in one bar. But I would write the accidentals in both directions. Your teacher will be happy. But if you ponder on the fact that they notate the accidentals in the descending scale and your teacher insists that they are necessary, this would be a kind of nitpicking. The best solution is to mark them in brackets as so called courtesy signs.