There is a good explanation of Bootstrap 3 and 4 Media Queries here at Bootstrap 3 breakpoints and media queries.
Bootstrap provides a great deal of flexibility to your project, but from minute details such as text justification between breakpoints, you will need to add a media query to your own CSS and apply the styles as desired.
So you might try something like this:
<div class="teacher-info col-xs-12 col-lg-8" >
<p class="ta-xs-left" style="font-size: 30px">
{{ teacher.personalInfo.name }}<br/>{{ teacher.personalInfo.surname }}
</p>
</div>
<style>
// Default to center the paragraph to center
.teacher-info p {
text-align:center;
}
// Large devices (desktops, 992px and up)
@media (min-width: 992px) {
// When the screen is larger than a tablet, left align the text
.ta-xs-left {
text-align:left;
}
}
</style>
Edit
In line with martinsoender's answer, I agree you shouldn't target modifier classes, and should add your own classes. This edit is to show how I would do that.
Essentially, I would add a class to the parent to denote what holds (teacher-info), then give the element I want to modify a class. In this case I create a class that looks similar to a bootstrap class. ta-xs-left ({text-align}-{Xtra-Small}-{Alignment}), then it can be reused wherever you need it.