We were able to trouble-shoot our gas oven before calling the repair man. Our oven reached temperature but did not reheat when it cooled down. Our troubleshooting included taking out the storage drawer and looking at the underside of the oven near the valve.
First check if you can see the flame when the oven is on.
Use an oven thermometer in the oven to test if the oven gets to the desired temperature first. Does it get close to the desired temperature and stay near there for your entire bake time? If it does, you may need to adjust the thermostat setting. (This should be in your manual. Many Frigidaire manuals are available from their support site: http://www.frigidaire.com/Customer-Support/Videos--Manuals/
Since our oven was reaching the set temperature and then not reheating, we had one person crawl under the oven and tap on the regulator when the oven needed to reheat. (We could see the ignitor spark.)
If the oven isn't heating at all, then the thermostat, the gas valve, controller or ignitor are suspects. Can you see the spark of the ignitor? Then it's probably not the issue. Similarly if you see the flame coming on several times during the bake cycle, it's not likely to be the valve. If you have a multimeter, you may be able to check the thermostat and controller for any breaks in the wire.
In our case, since the valve was failing, we ended up replacing the 10-year old range. (We looked at the price of a new range versus part and labor cost for the replacement. The part and labor was more than 50% of a new range.)
I hope this helps.