Read from the bottom up.
The bottom notes and the meldoy (usually upper voice somewhere) are the most important.
Figure out what's doubled. Conserve brain power.
Look for very easy band or orchestra pieces -- grade 1. Beginner ensemble music. You'll see the patterns there. Don't start with a full professional classical piece -- It's a lot more complicated.
I wouldn't mess with a school group. Just work on the scores yourself. I've never seen (or done) a conductor playing the score on a piano for an ensemble. It's just a way to study the score.
I'm not an expert at it and haven't done it too much. I know it gets easier and easier. It looks complicated at first, but there's not as much there as it appears -- You have to be good at transposing Bb, Eb, F mainly. And there are tricks, like knowing the lower instruments probably aren't tranposed

, most instruments sound lower than they're written if they are transposed, etc. I keep the key of the piece in mind and "see" the transposed parts as being "pulled up/down" from the 'real' notes.
I'm not satisfied with what I've done for reading/playing a score on the piano. Let us know what you figure out, like any tricks or tips. I get caught up with scanning vertically and getting the chord, doing that instantly (or faster than instantly) -- hence the top/bottom approach.
There are all the transposition games, but being practical -- you don't have to tranpose everything every which way.
For my 'harmonically challenged score reading' the advantage of the beginning pieces is that the harmonies are also simpler. I remember a nice ah-ha moment when I realized I kept coming up with the same chords.... in all the beginner pieces... I IV V.... piece after piece after piece.... shocking! :p
I think there's another thread about this on the site too.
The conducting classes in college, like all, are more like "Introduction to..." classes. Conducting is just as much work as playing an instrument. It's a different take on things too -- more analysis. There still is technique though too. The beginning conducting classes are like cookie cutter conducting, and then loads of transposition garbage thrown at you. You have to prepare real pieces just like you would piano. And better yet, have an ensemble to respond to you -- that sonic mirror for your gestures. But that's going beyond just score study.