Long time middle school teacher here so hopefully I can help somewhat about the curriculum. But it is very state specific and also depends on whether or not your school is a K-6 with a 7-8 somewhere else, or like my school a 6-12th grade. It also depends on whether your 6th grade is a self contained class.
Overall, the difference in curriculum isn't much between 6th and 7th. However, the way it is delivered is often very different. At my school, 6th graders have 3 teachers a day, 7th graders have 7 teachers a day in 45 min periods. They rotate classes, are expected to be organized and have it all together- turn in their work with one reminder, write in their agenda daily etc. We explicitly teach these skills along with study strategies and homework strategies in 6th grade.
We also often place 7th graders in Algebra. I have one 7th grader taking Geometry this year with the high school students. Because we have a 6-12 campus, that's easy. It's also easy because we are an arts school and ALL of the students are placed in arts classes based on ability. So it doesn't draw one ounce of attention to put a 7th grader in class with 10th graders. However, in a different setting, this would be more challenging.
All of that said, depending on the structure of your school, 6th grade is kind of like Kindergarten again. It's a review of skills for many students and it's also about "learning how to do school" in a different way. There isn't anything particularly challenging in the 6th grade curriculum that would leap out at me as something that would create a hole.
