OS X’s behavior regarding maximizing window size can be quite unpredictable and aggravating for those used to Window’s default maximize-to-screen. Shift/Command-clicking the maximize button doesn’t seem to get the job done consistently, either.
What you can use is RightZoom, a tiny utility to allow you to maximize your windows to fit the screen, and using the keyboard to boot!
1. Go to https://www.macupdate.com/app/mac/30591/right-zoom
2. Download RightZoom.
3. Open it by going to downloads folder, open folder, right-click on RightZoom, open, open.
4. Configure it to maximize your screen when pressing, say, Ctrl-Shift-M (I recommend using ‘Ctrl’, since it seems that with you can also toggle back to previous size).
5. Profit! Maximize screens to your heart’s delight.