Did you have other grasses that did well there?

Even fine fescues, though better in shade than many other grasses, need some sun to fill in and do well. Its always hard to gauge that (enough sun/not enough) over the internet.

"Sparse and not full" is not normal for any grass planted in a place where it will do well and seeded at an appropriate rate and given a good start planting wise.

How recently ago did you sow the seed and what was the watering schedule after you had sown it? Did you use a light dose of a nitrogen fertilizer or some other kind of "starter fertilizer"? Did you use anything to help retain moisture as a light mulch such a peat-moss or weed-free, relatively finely chopped straw? And most importantly of all, what did you do to ensure good contact between the seed & soil? Did you roll the soil with a lawn roller that was filled only 1/3rd of the way with water or sand, etc?

Kentucky bluegrass takes up to three weeks to germinate on its own and fescues are somewhere in the 7-14 day range themselves so it wouldn't be uncommon for it to be more than peach-fuzz but if you're looking for possible common mistakes we'll probably need some of the questions above answered first.

fine fescues and KBG take forever to establish.

I've tried growing grass for the past 2 seasons in these same areas in my yard. The areas are under Norway Maples. It gets at most dappled sun, but I gather it is the root system from the trees that eventually kills the grass. In the past, I've used sun/shade mix, the grass gets a good start, then by mid summer completeley dies. This time around, I used dense shade mix, tilled the soil, used only compost & PlantTone as my "fertilizer". I've been watering once each day for 2 weeks. The weather has been in the 40's overnight, 60's to 70s during the day. I lightly pressed the seed into the soil by rolling, but didn't cover it. Perhaps I needed to spread more seed?

Sorry Shelli, but, my guess would be the Norway maples are, between the shade and the aggressive root system I hear they have, outcompeting the grass. The good news is, it sounds like you have done all the right things to try to grow grass well.

I had some Norway maples I bought mis-labled. I removed them before they got big. But, the worse news is, I hear its pretty hard to grow much under them.

You might try some tough ground covers.

Good luck.

You are right about the root system of your Maples competing with your lawn for water and nutrients. I have a very healthy Fescu blend growing under and around sugar maples. First, put a mulch ring around your maples. It could be a circle, oval, kidney or any shape you desire. It should be at least one half the diameter of the drip line. Secondly, add organic material by mulch mow all your Autumn leaves into your lawn without smothering it. Pile chopped leaves up 6 inches thick in the mulch ring. Plant some shade loving plants there. Lilies of the valley work good. Fertilize and water inside the mulch ring well. Water your lawn evenly, deeply, but no more than once a week considering rainfall. Fertilize your lawn evenly but not excessively. Most of the lawn fertilizer should go on in the Fall. If you have access to compost then top dress once a year in the summer. Consider using organic fertilizers.
Bill Hill

Can you recommend an "aggressive" groundcover for under the trees that can stand up to a dog?

I would make suggestions if I had experience with Norway maples, Shelli, but, I have not.

I bet you would find some folks who have had that battle if you tried the groundcover forum on gardenweb. And, you might even try the question on the tree forum.

As many Norway maples as there are, there have to be alot of people with experience on what works best.

Vinca minor, evergreen "viney" groundcovers (Euonymus fortunei 'Colorata', Hedera helix, Liriope spicata, Pachysandra terminalis, etc.) or evergreen woody groundcovers (Juniperus conferta, Juniperus horizontalis, Juniperus procumbens, Microbiota decussata, etc).