Taking the time to thoroughly pre-teach the song will add emotional impact when viewing the film
The first time students recognize the song in the film there is a rush of excitement. Cool, I understand this! The second time that the song is played they have a deeper understanding of the context and there is no confusion concerning the danger faced by the main character. The third time, even the most immature students are appropriately shocked by the rebellion implicit in the actions of the boy and the priest. During the final credits, after a moment of silence in the dark as students emotionally recover from the ending, that first stanza is devastating. Qué triste, starts the singer, se oye la lluvia, and my students are choking back tears.
In past years I have paired the TPRS novel Esperanza with a documentary called Which way home?. They complement each other well to tell a story, but some of my students seemed especially hardened against the experience of immigrants. My school is located right on the front lines of the immigration debate with about 40% of our students hearing Spanish at home, over 50% living in poverty while another portion of mostly white students live behind the walls of a gated community the size of a small city. You might recognize some elements of my school community if you have ever read The Tortilla Curtain by T.C. Boyle. Our region made national news in 2014 when, just a few miles away, several buses of Central American immigrant children were blocked by protesters. 
Given the demographics of the community, I am not going to teach an immigration unit with a friendly debate at the end to understand multiple perspectives. The fire is just a little too hot here, and it is not fair to implicitly debate whether a portion of my students even have the right to be in my class. What I do like doing, however, is leading my students to recognize their common humanity with people that they have otherwise cast out as the others. Taking the time to thoroughly pre-teach the song helps students become emotionally involved in the movie.
This is the process that I follow to teach the song:
(1) On Monday I start by quickly telling the story of the song in very simple language that they can easily understand. I strive not to introduce much new vocabulary. I talk about the rain, and how much I like the rain. Then I talk about the casas de cartón built on the hillsides of many Latin American cities, including Tijuana (which many of my students have visited). When the rain falls, the water inevitably gets into the improvised shacks. When it rains hard, sometimes whole hillsides collapse. People die. I am always a little sickened by a jovial undercurrent among some students as they understand the reality that I am describing. Sucks for them, I have heard grinning kids whisper. I shut that down without hesitation, but I know that I am not winning hearts and minds yet.
(2) This is the step that provides the repetitions to make the entire song highly-comprehensible. For the 
Once they get really quick we do an “aural choral translation”: I turn off the overhead projector so that they cannot read the translations and, after hearing the part of the song, everyone translates aloud. It is more fun if they sing their translation to the rhythm of the song. A lot of repetition, but the pleasure of good music makes this bearable. Maybe even compelling. I like to be at the board (with a student controlling the computer) so that I can write the phrase in Spanish after it is played. The writing seems to bring it all together.
(3) At the end of the week I movietalk this music video made by students from la Universidad Francisco de Paula Santander. Now that we have heard the lyrics quite a few times out of context it is easy to point, pause the video and describe what is happening using known vocabulary and the lyrics. Introduce yourself and your students as parallel characters to get reps with verbs conjugated in the tú and yo forms. Together as a class write the story of the song on the board (not the lyrics, but the story).
(4) Once, as a fun Friday activity, we play this memory game, dividing the class into two teams. Students get very competitive about this game, but we only play it once. It is fun, but not nearly as good source of CI as the movietalk.
By the following week, when we start the movie, students have a really good grasp of the song. Students tend to identify with the child actors and that, surely, helps build their empathy. But I think the emotional impact that comes with understanding the lyrics at crucial moments in the film also plays a part in winning the hearts and minds of my students.
I have definitely withstood my share of criticism for this approach. “This is not CI”, “completely useless” and “waste of time” are some of the feedback that I have received from other teachers. I keep returning to these listening activities because, in my own classroom, I have found them to be the most efficient & effective way to teach a song to an entire class. When we listen to a Dominican bachata using this approach my students are already singing the chorus before we listen to the actual song. The repetitive nature of the activity, tightly connected to meaning, makes this activity successful. Moreover, it is quick– a five minute warm-up– and they are hearing and understanding the language spoken by a native speaker with a radically different accent than mine. Win-Win! Where is the disconnect?