I'm glad to see that you've discovered the Education.com Activities section. In addition to the page you visited, here are other activities you could do with your son to help improve his reading and writing:
 
http://www.education.com/activity/first-grade/reading/
http://www.education.com/activity/first-grade/writing/
 
Education.com also offers information centers for specific academic subjects. Here are the centers for reading and writing, as well as for top children's books:
 
http://www.education.com/topic/school-subject-reading/
http://www.education.com/topic/best-childrens-book-recommendations/
http://www.education.com/topic/learning-to-read/
http://www.education.com/topic/academic-subject-writing/
 
Each info center has a variety of articles and advice.
 
You might also consider some of the e-Learning offerings from Education.com's partners: http://www.education.com/e-learning/
 
I hope these resources are helpful to you and your son.

My daughter didn't really "latch on" to reading until late in second grade and now (wrapping up fifth grade) she reads well above her grade level...though has trouble reading books that are not of interest to her, even if assigned in school.  So based on my experience, there's isn't anything to worry about regarding your son.  There are ways to help, though, as dgraab listed.
 
I have no firsthand experience with this product, but I know three people who have tried the Headsprout reading system.  All three are well-educated smart tech-savy parents.  Education.com features this product (see the link below) and while this seems like a shameless plug for it, I respect the opinions of these friends and colleagues who use it with their kids.

Is he doing well in other areas such as math, science, music, art, PE, mechanics, etc.?  Sometimes if children are very strong in one of these areas, they tend to be weaker in the language area of the brain (left hemisphere).  You might want to consider some outside help in reading and writing for him.  Find someone who is a reading specialist that can tap into his particular learning style.  Now that summer is coming up, it is the perfect time to get him the help he needs so that he will feel confident and successful in the coming up school year.

Please Google "Dyslexia, Disability, and Deception: What Five Experts Say" for the case against sight-words, which is the central problem for so many kids.

Hello,
 
I would like to share this with you.  You can go to a website www.readingeggs.com.  It will help him well.  You can try it out with your son.  walk him though this reading program.  It awesome program.  My kids love it too.  
 
Good luck.