First, what is your argument? That single moms should finish their education? That single moms need to receive more benefits from the state? That single moms are the hardest workers?
Your thesis must contain whatever your argument is.
Some teachers want you to have a 3-part thesis statement. If yours is one of those teachers, you will also need to include the THREE REASONS YOU ARE RIGHT about your opinion.
For example, if your opinion is that Jiffy Peanut Butter is the best kind of peanut butter you must give 3 reasons why:
Jiffy Peanut Butter is far superior to any other type of peanut butter because it is the creamiest, most flavorful and least expensive.
Then, in your essay, you would have an intro paragraph, a para about how creamy it is, a para about how flavorful it is, and a para about how it so cheap and then a conclusion para.
Remember--this is an argumentation essay! You must focus on WHY YOU ARE RIGHT!