Like I mentioned, the only problem with the silver reflectors (aluminum foil, car reflector things, etc) is that they will usually put a very warm/orange cast over the subject and won't look completely natural. The most natural look for working with direct sunlight is white whether it be a white sheet, a white posterboard, etc. You can experiment with the aluminum/silver/reflective materials and see what you get. From when I've found, it's just way too orange and honestly it's just too harsh. The white does a good job of balancing the light color and diffusing light.
If you're farmilliar with your aperture control try lowering it (opening it). This will give you less depth of field and will blur out the background slightly which will direct more attention to the subject of the photo (the people in the portrait). An in-focus distracting background usually isn't the best thing when dealing with portraits.
If you're not familiar with aperture settings and such yet, don't worry. You're doing fine. You'll learn all about that stuff in your upcoming classes.