As an ultimate goal, we want to be able to think "I want to play an Fm scale" and the scale should be right under our fingers. We think "Let me play some notes of a Bbm scale now" and immediately our hand plays the right notes in any order. However, although a Bbm scale is a scale "derived" from the Db major scale, it has emphasis placed on Bb (and the other notes from Bb chord) and not on Db (This is part of the ingredients of a scale: a center of tonal gravity + a formula for subsequent notes. The first concept is not easily understood right away by beginners). So, when you think about the Bbm scale, your hand should visualize "Bb related notes" and if you need to make the brief mathematical analysis "What is the major scale from which Bbm is derived? Hm, it's Db. Ok, let me play the notes of Db but emphasizing the Bbm chord", then there is an unnecessary wasting of brain power.
Let me quote Gary Burton in a MOOC Berklee Coursera course (if you change Bm7b5 for Am, that's your question):
"Often students will ask this question about the seven modes: Since the same notes are used for seven mode scales (the B Locrian uses the same notes as the C Ionian, and so on), can we just think of the C Ionian, a more familiar scale, when we see a Bm7b5 chord symbol?
The answer is no. The reason the chord symbol is spelled as a Bm7b5 instead of a C major is to point us to the strongest notes, the chord tones, of the B minor harmony. The chord symbol is telling us more information than just the notes in the scale.
If the symbol says B minor something, then you will want to picture it, and think of it as B minor. If you have to first think of it as C major to find the scale notes, it creates an extra step in your thought process and distracts you from focusing on the important notes in the B minor harmony."
As an intermediate step, I am a proponent of learning 2 worlds that will serve as a basis for all basic structures: major and minor worlds. If you learn the G major scale, immediately learn Em and associate Em with the same key signature, although as a separate entity. Don't think of Em as a E scale with b3,b6,b7 and also don't use this kind of half-whole formulas (it's cumbersome if you want to skip notes). The idea of keeping these 2 scales in mind has the benefit of learning easily lots of other scales, changing just a few notes. If you want to practice the dorian scale, start with a minor scale and raise the 6th degree. If you want to practice the lydian scale, start with a major scale and raise the 4th degree. Most scales will be categorized as a part of the "minor world" or "major world". You can use a more fine-grained categorization and add the "diminished world", "dominant world", etc ... but now I digress :p