[Nathan]

I might write it as:

すこし日本語をべきょうしました。

Edit:

Maybe:
すこし日本語をべんきょうしていました。

If I'm not mistaken, the first would read like:
"I studied a little Japanese."
Whereas the seconds would be:
"I have studied a little Japanese."

I'm sure someone will come to correct me if its otherwise.