I'd like to suggest 2 sites for students to use to practice their basic math facts. Students will enjoy competing against themselves for higher scores, for 100% in a shorter time period, for solving harder problems with greater accuracy! For those who are struggling, they can practice their facts in the privacy of their own home and not have to feel threatened by others. You may have to encourage your students to practice the operation they are most uncomfortable with. We usually love to do the things we are already good at!
A+Math (http://aplusmath.com/) has several options but my favorite are the worksheets. First of all choose worksheets, then choose Online worksheets. Students can choose the operation then choose their level of difficulty. This is great for differentiated instruction. You could have an entire class working on this at one time and everyone could be working at their own level. If parents ask how they can help their child learn their math facts at home, direct them to this site. They can print off worksheet after worksheet for their child to work on. I have an idea the more they practice online though the better they'll become at their facts.
The other site I'd like to mention is Math Mania. There are lots of interactive math activities here! Students can choose the Math Facts Practice Online and time their efforts. I think students will be challenged by this to improve their scores and times. Explore this site for more games and drills.
Well, I just can't quit without mentioning another one of my favorites: aaamath.com. This is practically an entire year's worth of math curriculum. Great site for your students to get used to. They'll want to practice each concept that you introduce throughout the year.