I know a number of parents with AD(H)D children, including myself. Some of our children are medicated, some aren't. Indeed, at such a young age it's highly unusual for medication to be recommended -- instead, there are a variety of suggestions for behavioral interventions.
I've found that those suggestion are useful for neurotypical children, too. Any child can benefit from making activities interesting and engaging, redirecting bad behavior instead of reprimanding, having an organized schedule and structured life -- I find the advice to be useful for all three of my children, not just the one officially diagnosed as ADHD.
Home Behavior is something you can directly influence.
Some of the most common (and, anecdotally from my experience, effective) suggestions focus on establishing routine, providing a distraction-free space for homework or study, and breaking jobs down into smaller, manageable tasks.
Divide a big task or homework assignment into smaller, manageable tasks. "Do your homework" will work for my oldest child, but is an overwhelming demand for her younger brother. Instead we sit down and look at what the homework is (some reading, practice spelling words, two math sheets), plan what order it will get done in, write in places to take breaks (e.g. have a snack after finishing the spelling, then back to work).
Supervise. Stay nearby while the work gets done. Gently remind what the topic or task is if attention seems to be wandering -- something simple like, "How's your math going?" or "You're making good progress so far," or "I appreciate the effort you're putting in," helps snap his concentration back from that interesting leaf outside back to what he was supposed to be looking at. The goal is not to do the homework, and not even necessarily to sit there prompting for each addition problem -- provide the extra focus that's naturally lacking, be a resource to help adjust the homework plan if it turns out something is harder (or easier!) than expected, and just be a comforting presence so it doesn't feel like ME VERSUS HOMEWORK.
Concentrate on positive statements and praise. Kids with attention problems get used to constantly being told that they are bad at paying attention. Since they really are trying and just can't do as well as expected, this can lead to a lot of self-blame and low self-esteem. Finding opportunities to praise even the littlest successes -- once we learned about this strategy, I can't say it's completely turned my son's life around, but his bouts of crying over how he's "stupid" and "the worst" and "can't do anything right" have significantly decreased.
Research suggests that regular exercise can help with some ADHD symptoms. Encourage physical activity, whether that is through organized sports or activities, or just running around the backyard or a playground. (It also is good for general physical health, so why not?)
I have had very few conversations with my son about the Importance Of Focusing and How To Pay Attention. In retrospect, the majority of them were probably pretty insulting, because it's stuff that he knows almost instinctively -- if you don't listen to your parent or teacher, you'll miss important information (including, occasionally, "it's time to eat dessert, come here if you want some!"), so listening is important. He just wasn't able to pay attention well. He tended to be more receptive when I instead led with, "I know you have a hard time paying attention, and I appreciate it so much when you are focused." Such talks aren't useful when he's tired, being reprimanded for not paying attention, or interested in doing something else and therefore not really listening -- we save it for quiet time before bed or something like that.
School Behavior is a bit more challenging, since you don't have direct control over what the teacher can do in their own classroom. We've had one teacher who was incredibly strict and impatient with his behavior (which was horrible), and two who were more lenient and helped redirect him instead of immediately resorting to punishment (and he flourished). Part of this is just down to the teacher's personality and style, but the most useful tip I found was this:
The parent can help the child by talking to the teacher before the school year starts about their child's situation. The first priority for the parent is to develop a positive, not adversarial, relationship with the child's teacher. (1)
As long as you're working together to keep an eye on behavior, attention, and your daughter's progress, it's much simpler to deal with problems that may arise. Figuring out what works and what doesn't, and sharing what you've found effective at home, will help the teacher figure out what tools or techniques they can use in the classroom to keep her learning.
If you do have a official diagnosis of ADHD, then it's possible to put together an individualized education plan (IEP) that allows for longer time on tests, a quiet room to take them, or things like that. That isn't predicated on the child being medicated or not. (The terminology is almost certainly different in countries besides the US, incidentally.) So far I don't have one in place because we've had a lot more success establishing an "informal" IEP by being very involved with his teachers.
The resources below are geared towards ADHD or ADD, but I'll repeat that I think they're useful regardless of diagnosis. Whether she's got ADHD or she's just bored by the simplicity of the work being assigned, it can't hurt to try a variety of methods to help her focus more!
Attention deficit hyperactivity disorder | University of Maryland Medical Center
ADD/ADHD Parenting Tips: Helping Children and Teens with Attention Deficit Disorder
Parenting a Child with AD/HD
Not Paying Attention? Improve Listening Skills in ADHD Children at Home and School