Here's sort of gate checking 101.
You can gate check wheelchairs, strollers and usually ECVs and power wheelchairs. What people mean by gate checking is, you leave your (properely tagged) item at the gate and it is brought to the gate for you to claim at your destination city. During the flight, it is stored in a baggage compartment under the plane and it is one of the last things put on the plane when leaving and one of the first things removed when arriving at the destination.
Inquire about gate checking when you first check in. Sometimes, they will give you a gate check tag then.
Usually, they will say to ask the gate agent. As soon as you see the gate agent arrive at their desk, go up and ask about/get a gate check tag.
You don't want to wait until boarding because during the busy boarding time, there is more chance for error (more about that later) and also, (depending on the airport) there may not be time to get your item from the gate to where it needs to be loaded onto the plane.
At the gate, right near (kind of opposite) the door where you enter the plane, there is a door that leads to a stairway that goes down to ground level. Strollers, lightweight manual wheelchairs and ecvs that are not too big and/or heavy to be carried down the stairs can be taken out there for loading. Larger or heavier things (like power wheelchairs) need to be taken to an elevator to go down to ground level. The reason for getting to the gate 2 hours ahead of time is that at some airports the gate you are using may not be close to the elevator, so they need some time to get your item from the gate back down to the plane. That's why at some airports, you can't gate check ecvs or power wheelchairs.
The gate check tag is usually a neon color (ours have been greeen or hot pink) so it stands out and the baggage workers can see it is supposed to be delivered to the gate. When you hand over your ECV/stroller/wheelchair make sure the tag is securely attached, that it is visible and that you have folded your item as much as possible and removed/secured everything that might fall off, be broken off, etc. Any pieces you remove can be carried onto the plane and stowed in the overhead compartments (we usually removed DD's wheelchair seat and cushion (velcro and latched on), her footrests and her armrests. Those pieces DO NOT count as part of your carry on baggage allowance. If they are too big to fit in the overhead bin, they have to let you use the closet (If there is one - some planes don't have one), even if the closet is "reserved" for first class passengers.
At your destination airport, you should find your item delivered to the gate. This may take a while, especially if there are a lot of other gate checked items or if your item needs to be be sent to the gate using an elevator. We have been on flights when it took until the plane was almost empty for our DD's wheelchair to be brought to the gate; she was traveling with a manual wheelchair that was carried up the steps, so the delay was not due to using an elevator. We have also been on flights to Orlando where there were so many gate checked strollers that even though her wheelchair was delivered promptly, we couldn't get to it. So...... just sit in the plane for a while and relax while all the other people get out.
If you don't have a gate check tag, it is not filled out properly or it's not visible, your item won't be delivered to the gate. On our trip in April, we did see someone who brought their DD's wheelchair to the gate and carried her on. They were ahead of us. I didn't see a tag on their wheelchair and assumed either I just couldn't see it or they wanted it delivered to the baggage area. When we got off the plane, we could see the wheelchairs being unloaded. My DD's was brought up toward the gate. Another one (which turned out to be the other people's) was loaded onto the baggage cart. When we got off, the conversation I overheard made it clear that the other family had not known about gate check tags and thought that if they just left the wheelchair at the gate, that's where they would get it back. Usually, the people loading the plane are good about catching mistakes like that, but if you wait to ask about gate checking while you are getting on, they are busy and more likely to forget/make mistakes.
As was already mentioned, if you have a connecting flight, there may not be enough time between flights to have your item delivered to the gate at your connecting city and then put on the next plane you are flying on. So, in those situations, you might be forced to receive the item back at your final destination gate.
