A Level 6 Ranger with Practical Spellcaster has the 6th thrower level, that's right. But he still has the spells of a level 6 ranger daily: a spell of level 1. Spellcaster practiced has no effect on spells a day (nor known spells, for classes with spells) known at each level, the ranger is not one of these classes).
[Practiced Spellcaster] does not affect your spells per day or known spells. This only increases your caster level, which would help you penetrate SR and increase the duration and other effects of your spells.
When the Ranger becomes a Level 7 Ranger, his launcher level also drops to 7th – always 3 on guard levels, now +4 to Practiced Spellcaster. He always has only one first level spell. At rangers 8, 8, 4 and 4, he now has "0" level 2 spells, which means he is eligible for additional level 2 spells per day from a high Wisdom score. And in the 9th row, his launcher level remains the 8th position, since Practical Spellcaster can give at most +4 to a class, he gets 4 of his level of guard, +4 instead of Practiced Spellcaster.
To get the spells of a level 12 ranger you will need to actually be a level 12 ranger or at least 12 effective levels of ranger spellcasting among rangers and prestige classes that advance the spread of Ranger spells. There is no way around this throughout the match.
You can improve the casting of rangers, although
While a level 6 ranger will still have the day spells of a level 6 ranger and nothing will ever make him have the spells a day from a higher level ranger, you can change the caster of the class of rangers. In Dragon Volume 336 of the magazine contains the "mystic" variant of the ranger. This version gets the privileged enemy and combat style bonuses at more advanced levels than normal rangers, but generates more spells, at lower levels, than normal rangers. This is often recommended because casting spells is much more important than the exploits of the privileged enemy or bonuses, get those, just a little later, that's all.