Boost Persistence with Encouragement 
Research Evidence                       
Research indicates that student persistence in a STEM degree program is strongly influenced by faculty feedback - both positive and negative.  Since faculty comments can make or break a student's self-perception, a brief encouraging word from you can make the difference between a student switching majors or persevering. 

Often the only feedback students get is a written grade on assignments, exams, labs or projects.  If a good student gets a poor grade and/or spends considerable time on a homework assignment, they may begin to question their ability to succeed. For all students, but particularly women and underrepresented minorities who are used to excelling, this can undermine their performance and even their perception about their ability to complete a STEM program.
What To Do and Why It Works
Be honest if a student's work is under par, but students work harder if they feel YOU believe they can improve. Adding a message of encouragement with your evaluation can make all the difference.  

1) Encourage the class as a whole.
Email the class about a particular issue:

Hi Class -  
I am noticing that a lot of you are struggling with (_____), but here's a resource that can help. This step trips up a lot of people. Don't give up. (You can't forget those last two sentences!)

2) Encourage an individual student.
Use brief notes on written assignments, emails, or office hour discussions to let a student know you realize they are struggling. If you think they can succeed, let them know!

Hi Jean,
I noticed you spent quite a bit of time completing the assignment after people left. (Then add that extra boostI was glad to see you kept at it because I know you can get this.