Some of the difficulties that my year 9 have had with angles during this unit of work

In the Angle reasoning topic I think the focus needs to be on the reasoning and not so much the calculation. You can spend some time asking them to find the 3rd angle of a triangle, but understanding why an angle is 40° show a deeper understanding. I like to get students to draw triangles on dotty paper and then categorize them as isosceles, equilateral etc. This reinforces their understanding of each triangle.

Then i like to give students this task or similar:

Angles

After I gave the following questions which are angles in a triangle but in a shape that has been split into triangles.

Students were encouraged to use highlighters to make parts stand out and to cover up sections so the whole diagram isn’t overwhelming.

Angles in Triangles

Here are some resources on that in the ppt above

Angles on parallel lines

UPDATE:

Here’s a task I created because many of my students made assumptions about lines being parallel and just looked for alternate and corresponding angles in any lines regardless of marked parallel lines. Students can discuss when they might be or never can be and why.

Are they…