There is no doubt you could ID these plants and I'm sure you are a very good school teacher Floral. However, my point is, how could anyone make the determination that the student's assignment was to key out the plants and therefore withhold information -- particularly as this forum is well known as a resource and not as a sanctioning body of any type? The student may merely be using them to illustrate some aspect of the plants and requires a name to supplement his documentation. I'm sure he/she could have just as easily omitted to say it was in relation to an assignment and received an answer. In any case, I don't wish to make mountains out of molehills so I trust no-one has taken my comments too personally.

Something in the mustard family. Similar looking to Rorippa. https://www.minnesotawildflowers.info/flower/spreading-yellow-cress

Just be careful to keep it out of direct sunlight, they really seem to hate that, and you will probably lose more leaves. In the winter they barely need watering, despite the fact they their foliage would seem to indicate otherwise. Mine is in a north facing winter and it has really perked up from being in too much sun outside and is flowering.

Of course, keep in mind that 0.01% is still about 10 seeds per thousand square foot, and that's just what went down from the bag. And trust me, for some reason, even if the grass seed does not germinate, somehow every one of those 10 seeds will manage. Ask me how I know... Your soil had a seed bank in it from what was already there, and what blew in during the process and germinated...which is usually quite considerable in and of itself. Nature is, fortunately, not a sterile environment. What you're showing, however, isn't a problem from what I can see, either. It's just immature and hasn't attained its adult color yet. That's normal. But it can be hard to tell with the tips cut off. Some color variance is normal, particularly with seed that's not all that well-matched (cough-Scott's-cough). But it will get better as the grass ages. Some of us do object to the normal color variance in mismatched seed, but it's a personal preference. Let's put it this way--if the colors "Hooker's Green" and "Sap Green" mean something to you and seeing them close together is bothersome, then you're probably going to dislike the color variance in the lawn you just planted. If not, then no, you won't even notice it.