Building background knowledge.

As a math teacher I have always struggled with helping students build background knowledge especially those who skated through K to 8 by virtue of social promotion.  I know, I know, "we don't have social promotions but most school districts are still reluctant to hold students back, especially if the student is older than the others in his or her class.  This creates problems for the high school math teacher in that the students lack the necessary foundation to do well.  I know I do not have time to differentiate the way I'm supposed to nor am i always able to scaffold the way I should.  Due to living in a very rural community, I cannot plan a fully flipped classroom and expect my students to watch a video at home so they are prepared for the next day.  I could post videos on the school wiki but not everyone has unlimited data plans and thus may not be able to download and watch the videos.  Some times we run into the unreliability of the internet.
So over the past few weeks, I've been playing with using apps to help build or rebuild the foundation my students should have.  Today, I had my Geometry students use constructions lite to help build  perpendicular bisectors.  What is nice is they could watch a demonstration or they could slow the demonstration down to step by step so they could watch each step and think about it before they moved on.  After the demo, they practiced building a perpendicular bisector. One of the kids put in a perpendicular line and showed me he was done.  I was able to point out that he had not followed directions due to no "pencil" marks.  The next step after they practice both the perpendicular and angle bisectors is to apply these to actual triangles.  I need to play around with it to see if they can put in a triangle before they add the bisectors.