I enjoy reading to my children and listening to them read. It is wonderful to see them engaging in text. I have been listening to children read through my entire teaching career (over 22 years). I often begin with the incorrect assumption that children know all words presented to them. I have to remember to ask them if they know what certain words mean.
I am trying to make more of a focused effort on expanding your students vocabulary. I wanted to share some of the strategies that are currently helping. Some familiar methods would be telling your student what a word means, looking it up in the dictionary, and trying to guess what a word means from reading it in a sentence.
Another strategy that is helpful for visual learners is Semantic mapping or word maps. Here is a nice article that tells more. Basically, a word map is a visual organizer that promotes vocabulary. I find it helpful to use in science or social studies, and with beginning readers.
This is nice map for older elementary and middle school readers. Here is another one that would be excellent for science for older students. This is an article that shares how to use mapping with students in grades 4-6 in science. It is a teacher lesson with examples and a blank map. Lastly, here is one more that would work very well for 4th to 6th graders.
For younger students I like this map. It is very basic and easy to follow. You could also just take a piece of paper and fold it in fourths to have the same vocabulary map.
I would recommend trying to do this 2-3 times per month as a realistic goal. Try to focus on science and social studies for older learners and read-alouds for younger students.
There are many other methods, but hopefully these help your student to expand their vocabulary.