One thing I have done when I have a student in externship who seems to be faltering is to impress upon them how their performance during their externship directly affects their job prospects in the future. Just as it said in the course students have to be excited about future job prospects and about actually getting out into the workforce. I said to my student,  "whether you know it or not, right now you are beginning your professional career including your professional reputation which also includes future references for your resume". Students can be motivated by the thought that externship and every phase of their time spent during our program can directly affect future job prospects. The student seemed to get excited and very interested when I was speaking about his future career and potential job placement. In other words the more you can relate the thing the student is doing during class, lab or externship, to real life experience or future employment, the more motivated they become.