He studies the most of our children. Seriously ??? You really think this is the correct translation?
Yes, that is correct. (I'm a native speaker of AE.) Perhaps slightly better would be: "Of our children, she studies the most."
No, "of" is correct here. (Yopu coul also say "from among", but "of" is more idiomatic.)
Why can't this be translated as "He is learning the most of our children" ?
There is a difference between studying and learning. Studying refers to the application of effort to acquiring knowledge in a particular area. The goal of studying, then, is to learn something in that area. Consider, for example: "Because I studied German in college, I learned to speak it well."
I understand the difference between learning and studying in English, I don't understand it in Czech. Učit se literally means “to teach oneself” and I have seen it translated as “to study” and “to learn.” Frankly, I would think that “to teach oneself” is closer to “to learn” than to study, so why shouldn't both "she learns" and "she studies" be accepted?
No, učit se is normally really "study" though literally it is indeed to "teach oneself". But to learn is ro actually aquire some knowledge. We use the perfective naučit se for that, but it is not used in the present tense and it does not make much sense here.
Earlier, beži was translated: is running, and runs was marked as incorrect. Why isn't it here: is studying?
Please read the Tips and notes about determimate and indeterminate verbs (like běžět vs. běhat). Studovat does not have such a pair, it is used for both.
Thanks-- the (usually useful) Tips & Notes are not available on the phone app that I use. In any event, the verb used here was učit se.
While the Tips & Notes are not (currently) available in the apps, they are available on a mobile browser. You might give that a try to see if it works for you.
I am sure you are right, and they are hiding here somewhere, but on my Samsung S9+ (Android 9.0) with the Chrome browser I cannot find the Tips and Notes. ----Following Bonehead's suggestion, I checked again. If I log in through Chrome on the phone I see the light bulb in some skills, but not in others, so I guess it is as the developers meant it to be.
Hmm... I have a Samsung S7 running Android 8.0. When I logged in to Duo through Chrome, I find the T&N right where they are supposed to be. Click on a Skill and then, if you see a light bulb icon, T&N are available for that Skill; clicking on the icon will take you there If there is no bulb icon, no T&N are yet available. Hope it works for you! Any luck?