It is important for you to understand the purpose of a thesis statement before you can present one. Generally speaking a thesis statement informs the reader on how you plan to interpret or argue the subject matter. It serves as a sort of 'gameplan' for your paper. In order to develop a thesis statement you must take a stand on the topic.
Your topic is to compare the current economic climate in the United States with the economic conditions of the Great Depression...okay make a decision regarding the topic... are there any similarities? if so what are they? Remember a thesis statement takes a stand. Although I cannot write a thesis statement for you, I offer the following suggestions for your topic choices.
1. The connection between the reckless investment practices during the 1920's and those that preceded the November 2008 crash.
2. The role the banking industry played in the meltdown in 2008 as compared to the little to no regulation in the industry during the 1920's.
3. How one of the 'seven deadly sins' known as GREED consumed the financial markets during the 1920's and had a repeat performance in 2008.
Research the time periods, collect the information. If you use my suggestions to help streamline your efforts I think you will be successful in your efforts.
One other thing, I edited your question because you should never underestimate your capabilities nor deny yourself the accomplishment of a job well done due to your age. Just because you are in the 11th grade does not mean fanastic results are not possible....Good Luck !!!