There is no doubt that teaching high school students is much harder than university students due to lack of awareness, perception of lack of interest and so on.
Those are two very different things and so very difficult to compare. The level of difficulty will be measured by the interest of the teacher. For some what is stressful is a source of pleasure and vice versa. To those who feel attracted to that challange it will never be that hard. Fortunately, those differences do exist.
Each study has its own specifications. However, university education is characterized by a specialized education compared to secondary education, so I think there are no proper conditions for comparison between them.
There is actually a difference between high school teaching & college teaching not to be considered for the difference in the level of subject but also to be viewed between the student of two different faculties .
Professional college teaching due to the responsibility & of their understanding college student have become more mature which may help the professor to carry his profession teaching comfortably . In case of high school level student ,on positive issue for the teacher is that they know the student from the initial stage & for the student study in high school level in quite good cases they are not responsible for the career action . This certainly becomes the task for the high school level teaching student
A job with a low stress level, good work-life balance and solid prospects to improve, get promoted and earn a higher salary would make many employees happy.
Teaching is more than just imparting theoretical knowledge or practical skill sets which will help you earn a living. It is also creating the ability to live your life to the fullest and become what you were meant to be. And in that perspective, high school (and even earlier levels) become crucial because what they inculcate at these initial levels of their interaction with the world outside their own immediate families, is what will carry them to better life achievements. If they enter the college with an affirmative set of skills, they can become successful human beings, not merely rich and famous.
My experience is that it is not 'harder' to be either, merely that their responsibilities are different. School teaching creates the foundation on which a college teacher can build the future.
A career as a college professor isn’t for everyone. It requires a true passion for learning and an expert level knowledge base to even be considered for a college professor job.