Block scheduling turned out to be a surprisingly positive change when I grouped my choirs by gender.
Last year, because all Red Clay secondary schools went to block scheduling, I was (for the first time) able to schedule choirs across the grade levels. I had heard that segregating the genders was an advantage so I tried it, and it is one of the reasons I love block scheduling!
Here are 3 reasons why I've loved having my choirs grouped by gender:
1. Combining the girls across grade levels allows me to perform much more difficult music than is available for middle school mixed choirs. In addition, behavior problems really decrease. For some reason, the girls are much more rule driven so discipline problems are negligible. But, back to the music -- much more difficult and satisfying literature is available in Unison as well as SA, SSA and sometimes SSAA formats. Singing in foreign languages with better vowels is far easier as well.
2. Having a choir of just guys is a disciplinary struggle BUT the singing is remarkable. The guys get a chance to see how older boys have gotten through the voice change and how "cool" it is to sing. The literature can be challenging because the boy who was a soprano in September could be a tenor in January, but singing pop songs (in addition to classical literature) and adding "boy band" choreography is just awesome for them.
3. Word spreads and the choirs grow. Last year, I had 55 girls in an SSA choir. This year I have two choirs with a combined 130 girls! Last year, I had 20 boys in the Men's Choir. This year I have 41 and the counselor told me that more boys wanted to be in choir, but could not work out the scheduling. The guys love being in choir!
Clearly, after my experience this year, I highly recommend that you consider making the switch as well. And one more thing -- teaching SAB or SATB literature int he separate choirs and then combining for a concert works really well, and the singers learn the music a lot faster!