Running Rails 4.1.4 with the latest releases of haml, haml-rails, sass, and bootstrap-sass. For a user display, my HAML is as such:
.tutors-listing
.row
This is caused by skills with 2 lines of text or more. It's a well-known bug when using float property. Here is a little picture to understand :

[Bootply] The issue
Your first option is to force elements to have the same height :
.tutor {
height: 500px;
}
[Bootply] Force height
Your second option is to use a clearfix, and force the 5th element to be on a new line (same for the 9th, the 13th...) :
.tutors-listing > .row > .col-md-3:nth-child(4n+1) {
clear: both;
}
xs/sm/md/lg).col-xx-3)[Bootply] Clearfix