These pencils have a hard lead which makes it hard to highlight without going over the sentence several times. Try making the tip very flat on one end to get a larger surface area but I think the manufacturer just needs to make the leads softer.
This is the third set of highlighters that I have tried since the one I bought at a local book store ( closed) 10 years ago was worn down to a nub. These have leads so hard that in order to see the color on the page at all you have to bear down and risk tearing the page! The leads are very brittle and shatter when sharpening. The pencils are bright and the leads look bright too but to get a bright highlight takes a lot of work! These might be good for kids to color with. I just wish I knew who made the highlighter that I loved so much.