Anyone who teaches a primary grade will tell you how important it is for kids to know their combinations of 10. It leads to much more efficient strategies for addition and subtraction and will help a kid be more fluent with math. Let's see where combinations of 10 shows up in the Common Core
It first shows up in Kindergarten!
CCSS.Math.Content.K.OA.A.4 For any number from 1 to 9, find the number that makes 10 when added to the given number, e.g., by using objects or drawings, and record the answer with a drawing or equation.
In first grade it talks about kids using making 10 to help with addition and subtraction within 10
CCSS.Math.Content.1.OA.C.6 Add and subtract within 20, demonstrating fluency for addition and subtraction within 10. Use strategies such as counting on; making ten (e.g., 8 + 6 = 8 + 2 + 4 = 10 + 4 = 14); decomposing a number leading to a ten (e.g., 13 – 4 = 13 – 3 – 1 = 10 – 1 = 9); using the relationship between addition and subtraction (e.g., knowing that 8 + 4 = 12, one knows 12 – 8 = 4); and creating equivalent but easier or known sums (e.g., adding 6 + 7 by creating the known equivalent 6 + 6 + 1 = 12 + 1 = 13).
In second grade it is not mentioned by name but the little 2 has a comment on the bottom that says see the first grade standard above for a list of strategies
CCSS.Math.Content.2.OA.B.2 Fluently add and subtract within 20 using mental strategies.^{2} By end of Grade 2, know from memory all sums of two onedigit numbers.
Because of its importance, combinations of 10 is something you will see me working on in grades K2. I spend a lot of my intervention time with second graders (and sometimes older students!) who do not have strategies for addition facts working on combinations of 10. I have written about how I use
double flap cards, a simple
double sided chip game, and how I use
10 frames to work on this very important skill. I even wrote about how I extend this idea and work on
combinations of 100. Today I want to share with you a few of my favorite computer games that can be used on any PC or on a smart board that work on this idea of combinations of 10.
This is a student favorite and for a very good reason. It is so much fun! It also has multiple levels and is a race against time to complete a level before the balls all drop off.

Here is as look at level 1. You shoot the ball in the center at one of the balls on the outside that pairs with it to make 10. That makes both balls disappear. The object is to get rid of all the balls before they make it around to the hole and all disappear. If you do that successfully (and it takes a few times to get there when kids are first starting out) you get to move to level 2! 

Level 2 gets more challenging in the sense that there are some balls you can not reach. By the time kids make it to level 2, they are getting fairly fluent with their combinations of 10 and the game gets to be really fun and helps give them that extra push to fluency that kids really need. 

Level 3 builds a great deal of excitement over the 2 holes that the balls may disappear into. This is the level that is very tricky for kids to beat! 
I often use this game for combinations of 10 but it can also be changed to use for combinations of other numbers as well. I LOVE that this game represents equations and uses a missing addend.

You will see my target number at the top middle is set to 10. I can choose to set this number anywhere from 120 which makes it a VERY versatile game. Kids click and drag the correct answer into the box. I love the format of the equations. 
This one is less game like but still fun for kids and very effective at getting at the concept. I have
posted about this before but I do use it all the time for combinations of 10. (it also has an option for combinations of 5 and 20 so it gets a lot of use in various grades)

Simple but effective 
This is another student favorite. It is from ict games which is just a great resource in general. The object of the game is to get a long enough pipe (10 units) to bring water to the whale who is a bit land locked and help him escape to the ocean. I love that it has the units displayed for kids who still need to count. I often use this game for kids who still need some support with combinations of 10 although kids who are more fluent still benefit from playing as well.

The pipe at the top says 8 and is 8 units long. I can see that I need 2 more units to get to 10. See how this supports kids who are new to this concept? 

I successfully put a 7 pipe with the 3 pipe to make 10. Now the pond fills with water and the whale escapes to the ocean. 
I have previously written about
an iPad app that is very similar to this but this is the one I go to when I am on the smart board or a PC. This game actually does several things, so to work on combinations of 10, you need to click on fill along the left hand side. Then it simply asks you how many more counters you need to fill the frame (get 10). It is a very supported way for young learners to begin their work on combinations of 10.
How do you use combinations of 10 in your own classroom?