As I’ve referenced many times, I’ve not taught any of this elementary material to kids before and there are lots of struggles learning (and teaching) this material that are totally new to me. Often concepts that I think will be easy are difficult, and just as often concepts that I think will be difficult seem to be easy.
One thing that I’m really struggling to communicate to my older son right now is the importance of properly labeling diagrams. Maybe this is something that just about every student struggles with, I don’t know, but for sure I am struggling to communicate how important it is.
The struggle with labeling is illustrated well watching my son work through a problem about similar triangles from this morning. He does a good job identifying the geometric ideas in the problem, but has a hard time connecting the dots because nothing is labelled. It was really hard for me to sit on my hands and not help him through this particular difficulty today:
Once he does label one side of the square as “x”, the solution to the problem comes really quickly. I wish could find the right way to emphasize the importance of labeling diagrams properly – hopefully struggling through problems like this one will help get that lesson sink in.
Mike's Math Page 
Would be interesting to get the perspective of teachers with wider experience, but this didn’t seem like a long struggle to me. I think the clock seems to tick differently when you are sitting next to them and makes it feel like a much longer wait.
Actually, what held him up was that he didn’t identify all the relationships that were available. Labelling is one habit that helps address this, but it isn’t the only way.
Just saw this one and thought it could be a good challenge incorporating some of the topics you have recently been covering and the labelling issue:
Vecten Configuration
Before seeing this post, I’d never heard of this theorem, but it is very nice.