Beginners can play in tune. Really...they can. And they WANT to play in tune. No one wants to sound bad. I learned this while studying the Suzuki method as my son (age 4) began his violin lessons. He was taught to place his fingers perfectly and he wasn't to pull his bow until his fingers were set. That means, we had to pause after every 'tukka tukka stop stop' to place the next note before pulling the bow again. With this careful practice, my son never had the chance to play out of tune. Soon enough, he developed the muscle memory to land his fingers in tune add we no longer had to pause between pitch changes. In a beginning orchestra setting, we may not be able to physically check and move each student's finger to the right place, but we can use tapes for a guide. Students in a classroom are older, anyway...and they need to learn how to monitor their own playing. When students are struggling to get pitches in tune, I have found it helpful to step back and use the Suzuki strategy. Set. pull, listen. Does it match - is it in tune?
Recently, I did a warm-up with my beginning orchestra class and it helped their overall intonation so much that I started doing it with all of my groups. We often warm-up with finger patterns and scales...this is just a new way to approach the patterns. We drilled only 3 notes at a time. In my experience, students are most often out of tune when playing half steps. This little drill helped students fix those intervals and they performed with better intonation through the entire rehearsal after playing it.
I don't have students read the sheet music for warm ups because I want all of their focus to be on their fingers, half steps, intonation, tone, bow placement. etc. They easily pick up on this simple warm-up by rote.