Discovery Education is a website that has an entire section dedicated for teachers. Here, teachers can find tons of resources to use for lesson plans they may want to implement in their classroom. In particular, under the lesson plan library, I found a lesson that teachers can use to introduce students to ocean currents and how they function. Although this lesson plan is designed for grades 6-8, I believe it could be valuable for younger grades if teachers take it and design it to fit their classroom and refer to their grades standards.
Understanding Oceans (Ocean Currents) – Discovery Education