It's non-zero value, but we can't say it's the market-clearing price for their services. And anecdotally the quality of that education is compromised.
Student-athletes in the serious football and basketball programs spend a lot of their time at practice. During the season, travel to away games eats up much of their free time. They're "encouraged" to take only easy courses. There are reports of grading corruption so their GPA is high enough to remain eligible to play.
They still get admission to a university with lowered standards and a credential at the end of the day. A lot of these scholarship athletes aren't college material and wouldn't get in otherwise. There's some value there.
It's kind of like rich kids who are bad students paying for admission into elite schools. Obviously there's value, otherwise they wouldn't have their parents pay for it.
Like I said it's non-zero value. But is it more value than a fair wage, negotiated without artificial restrictions? Why can't they grant the athletes admission and give them the option of either studying tuition-free, or pay tuition but earn a salary for playing?