"Our board is going in a good direction."
Translation:Nia estraro iras en bonan direkton.
I think it's precisely because "iras" shows direction that you use the accusative markers (to agree with the idea of the verb).
The main idea is that it needs to show direction towards (or away from), and that can be metaphorical as well as factive (from a place to a different place, regardless of whether they're physical or not).
In that case, would "Nia estraro iras al bona direkto." also be counted as correct? (I cannot check this out on the test, unfortunately.) "En" just doesn't seem to be the word one might use for a direction or path: Mi iras norden ≠ Mi iras en la nordon ≠ Mi iras al la nordo. For a location, certainly: Mi iras Londonen = Mi iras en Londonon. = Mi iras al Londono. But it might be my English background that is causing me to doubt the sense of "direction" being something one can move into. Once someone is moving, there's already an implied direction (to a neutral observer standing somewhere, as Einstein might put it.)