How can we better understand and serve HLLs?

"Most teachers have not been trained to work with students who already speak
or understand the target language or who have a strong connection with it. Similarly, language teachers brought in from countries where the languages are spoken have little or no idea about bilingualism and about the language competencies
of heritage students who have been raised in this country." (Valdes, 2001) The previous quote got me thinking about the fact that our training sessions at UNM for teaching Spanish are a few days long and they occur days before we embark in the task of teaching Spanish to college students in the Basic and Intermediate levels. While on the job, we take a methodology seminar for one semester. My questions are: Is this enough teaching training as to be fully immersed in teaching or be able to apply approaches to bilingualism and language competencies of heritage students ? Should TAs interested in teaching SLLs also take a a class on how to teach HLLs since HLLs in many cases opt to attend SSL classes?