Noticing this issue was one of the first things (of several) that started me down the path of really investigating the differences between male and female (reminder: I'm still single). I work with my church in a Wednesday night children's ministry focused on Bible memorization (Awana, for those who know of it), and I noticed over several years that the girls were consistently completing the curriculum handbooks at a higher rate than the boys, which didn't make any sense to me. Furthermore, the boys were more likely to be on ADHD meds, or to have apathy about the whole program, or to cause "trouble" for various reasons. This was all very confusing to me, because it was pretty much the opposite of my experience (e.g. I was home-schooled, then got straight A's throughout college), so I started wondering about how boys were being treated by society and how I could help them.
Digging further, I realized that this was a wider phenomenon in our culture, with schools more focused on helping girls while abandoning boys. One excellent book about this that I started reading last year (though I haven't made it even half-way through yet) is Christina Hoff Sommers' "The War Against Boys: How Misguided Feminism is Harming Our Young Men". It was published in 2000, so all of its stats are from the 80's and 90's, but I'm sure things have only gotten worse since then. From there, I started falling into watching logical tear-downs of feminist ideology on youtube, and ended up distracted by that.
Bottom-line: I'm still not sure how to best help boys memorize, but I'm more willing to try different approaches -- and to encourage and help them to take responsibility for their own progress, while allowing them space to fail if they don't. I had one boy tell me this year that I was "savage," and the same boy also tell me that I was his favorite teacher. So that's something, I guess? Unfortunately, I'm a bit disheartened that Awana has begun changing its curriculum (again) to include a "discussion" time, because I haven't seen that sitting around in a circle talking about things is a particularly useful way for most boys to learn.